Monday, August 31, 2009

The arch in St. Louis is welded stainless steel. I took this photo of it after my trip to the top. The ride to the top is inside a space age capsule that holds five. At 630 feet tall, I calculate I could see 30 miles to the horizon.

Saturday, August 29, 2009

DALPro is a physicaly small shop, but they sell around the world. The original company was called Kepro, after the owner. They went out of business in 2004 and D and L took over. A Kepro board was used onboard the first space shuttle launch. I'll have to find out where. It's it amazing that the PCB materials you can purchase today for your projects was good enough for a manned space launc in 1981?

Friday, August 28, 2009

I begin the process of making printed circuit boards (PCBs) by using a programm called Ares Lite. The file is printed as a copper mask and transferred to a presensitized sheet of copper clad. The copper clad is manufactured by a company named DALPro and they're based in St. Louis. This weekend I'll get a chance to pay them a visit and I'll post my impressions.

Thursday, August 27, 2009

I'm soldering a smart proxmity detector PCB. It uses a PICAXE-08 and will communicate with the robot it is attached to. The idea is that its PICAXE flashes two IR LEDs in sequence and looks for a sign of a reflection from the 40 kHz IR detector. The result is sent to the robot controller as a serial message. The PICAXE can operate the IR LEDs at a range of frequencies, allowing the proximity detector to estimate distances to obstacles. Since there are two IR LEDs, the proximity detector determines whether the obstacle is on the left, right, or both sides.

Wednesday, August 26, 2009

I'm still plugging away at soldering the new flight computer together. It uses an I2C memory chip to store data in EEPROM. A MicroTrak 300 is the onboard transmitter. The goal is an affordable solder kit to help new groups get near spaceborne.

Tuesday, August 25, 2009

I just received a new flight computer PCB. This one uses a PICAXE-28X and reads GPS data in background. Its built-in radio is a 144.390 MHz transmitter by Lemos. The pads for the antenna connector are good but for one. I'll drill it out for this test, but will modify it for the production boards.

Monday, August 24, 2009

To avoid taking up volume inside the BalloonSat airframe, I cut channels into the walls of the Styrofoam and glue my tubes and dowels. It takes a little pre-thought when designing, but the result is a BalloonSat with the maximum interior volume.

Sunday, August 23, 2009

Lowes is selling sheets of 1/2 inch thick Styrofoam for $10. The sheets are four feet by eight feet and made from the "softer" blue Styrofoam. With 32 square feet of the stuff, you can make an entire fleet of BalloonSats.

Friday, August 21, 2009

Really hot hot glue can melt Styrofoam. If you can't adjust the temperature of your glue gun, try unplugging it on occasion. The glue, when it's too hot, metls into Styrofoam. The result is poor contact between sheets of foam.

Wednesday, August 19, 2009

I've noticed a "grain" in Styrofoam. I suspect it extruded and that stretches out the polymer in the polystrene. When you cut Styrofoam with a dull blade, it creates chunks more readily if you cut across the grain.

The moral?Cut only with a sharp blade and only along the grain if you absolutely must use that dull blade once more.

Tuesday, August 18, 2009

Not only does hot glue do a good job assemblying the sides of an airframe, it's also great for covering copper traces. That's because the plastic in hot glue is a very good insulator. It tacks well and if it needs to be removed, you can work off (mostly by peeling it off).

Sunday, August 16, 2009

If you use power poles for your battery connections, be sure to backk fill them with hot glue. This prevents anything small and pointy from creeping into the back of the connectors. Everything electrical in a near spacecraft needs protection from shorts. It's really bad news to have a short at 100,000 feet.

Saturday, August 15, 2009

I don't use plastic battery holders for critical applications, it's too easy for a cell to pop out. Instead, I use battery "snaps", or plug in connectors. The battery can move around at the end of its cable, but since the cable is flexible, there's no strain on the connector (unless the battery falls out of the airframe (in which case, you've got a lot of other problems).

The kinds of connectors I've used are Anderson Power Poles and Dean's Connectors.

Friday, August 14, 2009

Rechargable lithiums from cell phones are available through surplus electronics catalogs. Be sure to purchase a recharger with them, since lithiums need their own charger to maintain their lifespan. You'll need to solder connectors to the batteries since there aren't battery holders made for them (the phone has its own set of tabs that connect to the contacts in the battery case). I've found three electrical contacts int eh batteries I've nmodified. Two are needed for charging, the third is a control circuit to prevent over charging or over heating.

Thursday, August 13, 2009

It can get cold inisde a BalloonSat. Alkaline batteries will have a problem providing current in high drain cases. Normally I use lithium batteries because they can handle -60 degree F temperatures. Good photo-lithium batteries are avilable at Walmart and Target in the camera department.

Wednesday, August 12, 2009

The launch and descent after balloon burst can be very chaotic. To prevent the BalloonSat's innards from being bounced to death, either bolt equipment into place or use a filling material.

Bolting can be done with #2-56 hardware to keep it light, but you'll want washers to make the head of the bolts larger. Try using plastic (20 mil thick?) that you can purchase from hobby shops that sell model trains (or other construction type hobbies).

Tuesday, August 11, 2009

Don't use really tight rubber bands to close a BalloonSat hatch. They'll pull too tight and deform the Styrofoam airframe. They're also too difficult to put back on (esspecially if it's cold and the launch crew is wearing gloves). It's bhetter to double up the rubber bands.

Monday, August 10, 2009

Dowels protruding from the airframe are great for wrapping rubber bands around. The dowels should run through the back of the airframe and extend another 1/2 inch beyond the side of the airframe. Cut a channel as wide as the dowel's diameter and glue the dowl inside. That way the dowel doesn't take up any of teh volum inside the airframe.

Sunday, August 9, 2009

It may be necessary to open a BalloonSat at the launch site (say to load an experiment or insert a battery). A hatch held closed by rubberbands is ideal for this. Rubberbands can be snapped on and off quickly and with no tools - ideal for the rush during launch prep. I've tested rubberbands on many flights and have discovered they hold up wel for the cold, vacuum, and ultraviolet of near space.

Saturday, August 8, 2009

To keep BalloonSats from slipping down their link lines, tie knots in them and connect split rings through the knots. That way there is no force tugging on the BalloonSat. They're free to slide around on the link lines. If you physically restrain the BalloonSat, then the post-burst chaos could rip them apart or otherwise damage them.

Friday, August 7, 2009

Link lines are the cords that tie one or more BalloonSats to a near spacecraft. So they don't tear a Styrofoam BalloonSat apart, there must be a race way attached to the BalloonSat for the lines to run through. Some groups have used flexible vinyl tubing and others ink pens with the guts removed. I prefer to use styrene plastic tubes. They come in a variety of sizes and are available at many hobby stores that sell airplanes, cars, models, and rockets. A 1/4" diameter tube seems to be ideal. Best of all, the tubes are very long and can be cut to the proper length. That way your BalloonSat dictates its proper size, not the tubes you have on hand.

Thursday, August 6, 2009

I prefer having at least three lines running through a BalloonSat. A single line connecting the BalloonSat to the rest of the near spacecraft leaves it swinging and twisting around too much. The extra cords dampen out the motion leaving images with less blurring from motion.

Wednesday, August 5, 2009

Another simulation that's important is landing. A parachute landing has a speed of about 10 mph. That's the speed something dropped for 0.5 seconds will reach (10 mph is about 15 fps and that's close enough to 16 fps which is reached in 0.5 seconds at an acceleration of 32.2 feet per second squared). In 0.5 seconds, an object falls roughly four feet (distance = 1/2 * 32.2 * 0.5^2). So to simulate a parachute landing, drop the module (BalloonSat) from a height of four feet.

If it can land without blowing apart, then you'll probably get the experiment back in one piece.

Monday, August 3, 2009

A burst balloon in near space quickly deccelerates and starts its free fall down. In about five seconds, the near space craft will reach its maximum speed and have fallen 500 feet (based on data from flight NearSys 09D). Video footage shows the parachute opening and closing and the remains of the balloon whipping around. Its very traumatic and its accompanied by lots of jerk (changes in acceleration).

A BalloonSat not properly designed for the post-burst chaos is liable to open up or fall apart.

To test for this situation, tie cords to a broom handle and suspend your total BalloonSat (batteries included) from the cords just like it would be suspended from a near spacecraft. Hold the end of the broom handle away from your face and give the appartus a good shaking.

If your BalloonSat holds up, it's ready for the balloon burst and descent.

Sunday, August 2, 2009

An easy aspect of near space to simulate is its intense cold. A styrofoam cooler packed with dry ice does a nice job. But don't let the experiment actually touch the dry ice. Use a cookie rack to hold the experiment above the dy ice. Even colder temperatures can be reached if you add a fan or two to circulate the air Run their power cables outside the enclosure as there's no need to chill the power source of the fans.

Expect temperatures to drop to at least -60 deg F on ascent to near space. Your dry ice chamber shuld be able to get close. Brrrrrr!!!

Saturday, August 1, 2009

I submitted an article to Nuts and Volts about the environmental test chamber I built. Read it to see how you can convert an airtight flour cannister into a ultra-cold and low pressure test volume for experiments.